This invention relates to a process of using "seed crystals" for growing highly textured bulk quantities of superconductors such as single large domain RBa.sub.2 Cu.sub.3 O.sub.7-.delta. where R is a rare earth, La or Y. More specifically, the invention relates to melt processing high T.sub.c superconductors using seed crystals of lower cost but significantly larger surface area than previously available. The seed materials are a laminate of an oxide compound such as, for instance, SrTiO.sub.3, LaAlO.sub.3, or the like, which have high melting or decomposition temperatures above those of the high T.sub.c superconductors but are readily available and of low cost and which are not T.sub.c superconductors themselves onto which is deposited a thin film of NdBa.sub.2 CuO.sub.7-.delta. or SmBa.sub.2 CuO.sub.7-.delta..
Large single domains of YBa.sub.2 Cu.sub.3 O.sub.7-.delta., materials show high levitation forces because of their size and because of their good flux-pinning strength due to large numbers of small pinning sites. The materials show promise in practical applications requiring levitation or high magnetic fields, such as fly wheels for energy storage, high field magnets, magnetic resonance imaging and efficient electric generators. Previously, SmBa.sub.2 Cu.sub.3 O.sub.x as well as Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y have been used as the seeding material during the melt-growth process in making large single domain 123 material (YBa.sub.2 Cu.sub.3 O.sub.x).
More particularly, SmBa.sub.2 Cu.sub.3 O.sub.x (Sm 123) had been used, but this material has a serious defect in that Sm 123 has only a slightly higher melting point than the bulk (YBCO) 123 material and, therefore, the seeds of Sm 123 often melt during the process. This is undesirable, since the purpose of the seeding material is to provide solid particles to facilitate the crystallization of the melted 123 material during the melt-forming process.
It has been found that Nd 123 forms a solid solution in the form of Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y and was previously thought to be unsatisfactory as a seed material, but a co-pending patent application Ser. No. 371,931 filed Jan. 12, 1995, now abandoned, assigned to the assignee herein, the disclosure of which is herein incorporated by reference, teaches the use of the Nd 123 material as a seed for preparing bulk superconducting material.
The problem encountered in using either the Sm or Nd 123 materials as seeds is that both of these materials are expensive to produce as single crystals and only relatively small crystals have been able to be made. These problems limit the use of the Nd 123 material even though the Nd 123 material is particularly advantageous because of its relatively high melting temperature compared to the melting temperature of bulk superconductor being prepared so that the Nd 123 material does not melt during the high temperature processing of the RBa.sub.2 Cu.sub.3 O.sub.x material.
It has been found that large surface area Nd 123 or SM 123 seeding material can be made inexpensively with suitable inexpensive with suitable readily available substrate materials such that large domain material can be prepared by using the Nd 123 or Sm 123 as thin films in combination with cheaper oxides as substrate materials. The thin films Nd 123 or Sm 123 can be deposited on the oxide substrate with any conventional deposition technique. The advantage of the present invention is that large surface area Nd 123 or Sm 123 can be made at low cost to provide seed material to make large single domain R 123 superconductors, where R is La or Y.